Electric circuit breaker with improved tripping means including a heater strip in the thermal tripping means and adjustable air gaps in the magnetic tripping means



3,345,591 NG L LEONARD ET A Oct. 3, 1967 1. L

ELECTRIC CIRCUIT BREAKER WITH IMPROVED TRIPPI MEANS INCLUDING A HEATERSTRIP IN THE THERMA TRIPPING MEANS AND ADJUSTABLE AIR GAPS IN THEMAGNETIC TRIPPING MEANS Filed J ne 29, 1966 3 Sheets-Sheet l fwerznJamal/Lawn@ Zdw 9:

Oct. 3, 1967 J. H. LEONARD ET AL 3,345,591

ELECTRIC CIRCUIT BREAKEH WITH IMPROVED TRIPPING MEANS INCLUDING A HEATERSTRIP IN THE THERMAL TRIPPING MEANS AND ADJUSTABLE AIR GAPS IN THEMAGNETIC TRIPPING MEANS Filed June 29, 1966 3 Sheets-Sheet 2 @'4' ZE -f@Si 2f Jy @Jvw wf Oct. 3, 1967 1 H LEQNARD ET AL 3,345,591 D TRIPPINGRIP IN THE THERMAL ABLE AIR GARS 1N ELECTRIC CIRCUIT BREAKER WITHIMPROVE MEANS INCLUDING A HEATER ST TRIPPING MEANS AND ADJUST THEMAGNETIC TRIPPING MEANS 3 Sheets-Sheet 3 4 Filed June 29, 19 zg/91,

United States Patent ELECTRIC CIRCUIT BREAKER WITH IMPRVED TRIPPINGMEANS INCLUDING A HEATER STRIP IN THE THE TRIPPING MEANS AND ADJUSTABLEAIR GAPS IN THE MAG- NETIC TRIPPING MEANS `lames H. Leonard and WilliamH. Woods, Cedar Rapids, Iowa, assignors to Square D Company, Park Ridge,Ill., a corporation of Michigan Filed .lune 29, 1966, Ser. No. 561,456 6Claims. (Cl. 335-23) This invention relates generally to electriccircuit breakers, and more particularly to a circuit breaker havingimproved tripping means.

An object of the invention is to provide an electric circuit breakerhaving improved thermal and magnetic tripping means.

Another object is to provide a multipole circuit breaker having a singleadjusting means by which the air gaps in the magnetic circuits of themagnetic tripping means of all the poles may be adjusted.

A further object is to provide an improved arrangement of parts withrespect to the thermal tripping means of a circuit breaker.

In the drawings, FIG. 1 is a reduced front view of a circuit breakerconstructed in accordance with the invention, certain portions thereofbeing indicated by broken lines;

FIG. 2 is a fragmentary front view of the circuit breaker of FIG. l withthe cover and handle removed;

FIG. 3 is a fragmentary front view of a terminal strap, bimetallicstrip, heater, and contact arm sub-assembly of one of the poles of thecircuit breaker of FIG. l;

FIG. 4 is a fragmentary sectional view taken generally along the line4-4 of FIG. l;

FIG. 5 is a fragmentary sectional view taken generally along the line5-5 of FIG. 1;

FIG. 6 is a sectional view taken generally along the line 6-6 of FIG. 4;

FIG. 7 is an enlarged fragmentary sectional view taken generally alongthe line 7 7 of FIG. 6;

FIG. 8 is an exploded perspective view of the air gap control member,cam, and air gap adjusting crossbar of the circuit breaker of FIG. l,the crossbar being fragmentarily shown;

FIG. 9 is an enlarged fragmentary sectional view taken generally alongthe line 9 9 of FIG. 6;

FIG. l() is a view similar to FIG. 9, but showing the partsrin differentpositions; and

FIG. 11 is a bottom view of the' air gap control member and cam.

FIG. l shows a three-pole circuit breaker 20 constructed in accordancewith the invention and having a casing ncluding a cover 21. An operatinghandle 22 protrudes through an aperture 23 in the cover 21, the coverbeing provided with suitable ON and OFF indicia.

The cover 21 is secured to a base 24 (FIG. 2) by a plurality of screws25 received in suitable apertures in the cover. Further, the cover 21 isprovided with a plurality of apertures 26 affording access respectivelyto a plurality of socket-head clamping screws 27 which respectively formparts of a plurality of electrical connectors by which a plurality ofelectrical power conductors (not shown) may be connected to the circuitbreaker 20.

The cover 21 is also provided with an aperture affording access, bymeans of a t-ool such as a screwdriver (not shown) or the like, to anair-gap control member 2S provided in accordance with the invention andhereinafter described. The control member 28 controls the position of anair-gap adjusting crossbar 29 hereinafter described.

:3,345,591 Patented Oct. 3, 1967 ICC Adjacent the control member 23, thewith suitable LO and HI indicia.

A center pole space of the circuit breaker 20 is provided with operatingmechanism substantially identical to that disclosed in copendingapplication, Ser. No. 375,571, tiled on J une 16, 1964, to whichreference may be had for a fuller disclosure. As shown in FIG. 5, thecover 21 holds the handle 22 on a generally U-shaped handle eX- tensionmember '30 opposed leg portions of which straddle and are pivotallymounted respectively on a pair of frame members 31 and 32 (FIG. 2)secured to the base 24. The handle extension member 30 pivots on a pairof rivets 33 disposed respectively in the frame members 31 and 32, onlyone of the rivets 33 being shown in FIG. 5.

Opposed leg portions of a generally U-shaped releascover 21 is providedably latchable cradle mem-ber or trip lever 34 are pivotally mountedbetween and respectively on the frame members 31 and 32 by means of apair of rivets 35 disposed respectively therein, only one of the rivets35 being shown in FIG. 5. The frame members 31 and 32 are joined -by atubular stop pin 36 secured in place by a pair of screws (not shown)extending respectively through the frame members 31 and 32 and threadedrespectively into opposite ends of the stop pin 36.

A pair of upper links 38 are pivotally mounted between `and respectivelyon opposed leg portions of the trip lever 34 respectively by a pair ofrivets 39, only one link 38 and one rivet 39 being shown in FIG. 5. Theedge of each upper link 38 is recessed at the end thereof opposite itsassociated rivet 39 to receive a toggle pin 40 held in the upper links'38 by a tension spring 41 hooked at one end to the toggle pin 40 and atthe other end to the handle extension member 30.

Pivotally mounted adjacent one end on the toggle pin 46 is a lower linkmember 42 having a drive pin 44 pivotally mounted therein adjacent itsother end. The lower link member 42 includes two parallel Hat elongatedlink portions connected together generally centrally of a longer edge ofeach of the link portions. Thus, the lower link member 42 is generallyU-shaped in cross section in a portion thereof between the toggle pin 40and drive pin 44.

As previously pointed out, the leg portions of the handle extensionmember 36 are respectively mounted on the rivets 33 on the outer sidesof the frame members 31 and 32. On the inner sides of the frame member31 and 32, a drive arm 45 is pivotally mounted adjacent one end on theinner end portions of the rivets 33. A Contact arm mounting pin 46 ismounted in the drive arm 45 adjacent the other end thereof. The drivearm 45 is shaped similarly to the lower link member 42 in that a centralportion thereof is generally U-shaped in cross section and the legportions thereof are elongated in a direction parallel to the bightportion thereof, each of the leg portions being pivotally mounted on oneof the rivets 33 and opposite end portions of the drive pin 44 and thecontact arm mounting pin 46 being mounted respectively in the legportions of the drive arm 45. As disclosed in thev aforesaid copendingapplication, one end portion of the drive pin 44 may be adjustably keyedto the drive arm 45 and the portions of the pin 44 received respectivelyin the opposed link portions of the lower link member 42 may be providedrespectively with eccentric cams, whereby the eective length of theconnection between the toggle pin 40 and the drive arm 45 may beadjusted.

A movable contact arm 47 carrying a movable contact 4S adjacent one endis pivotally mounted on the pin 46. The bight portion of the drive arm45 is riveted or otherwise secured to a contact arm crossbar 56 formedof insulating material and preferably reinforced with a metallic strip51. A contact pressure spring 52 biases the contact arm 47counterclockwise as viewed in FIG. 5.

The trip lever 34 is normally held in a latched position by engagementof a tongue 34a provided on the bight portion thereof with the bightportion of a generally U-shaped intermediate latch member 54 the legportions of which are pivotally mounted on a pin 55 mounted adjacentopposite ends respectively in the frame members 31 and 32. Theintermediate latch member 54 is normally held in a latched position byengagement of one of the leg portions thereof with a latch plate 56secured, as by a rivet 56a (FIG. 6), to a trip bar 57 pivotally mountedin a pair of spaced intermediate wall portions 24a (FIG. 2) of the base24. The wall portions 24u and a corresponding pair of wall portions 21aof the cover 21 divide the casing of the circuit breaker 20 into threeside-by-,side pole spaces or compartments.

The contact arm crossbar 50 extends into the two outer pole spaces ofthe circuit breaker 20. Each of the opposite end portions of thecrossbar Si) has a generally U-shaped mounting bracket 58 (FIGS. 2 and4) secured thereto, the bight portion of each bracket 58 preferablybeing riveted to the crossbar 50 and an extension 58a of the bightportion being wrapped partially around the crossbar, as shown in FIG. 4.Opposed leg portions of each bracket 58 carry a mounting pin or rivet59. Each of the outer poles includes a movable contact arm 47, a movablecontact 48, and a biasing spring 52 identical with those of the centerpole, the contact arms 47 of the two outer poles being pivotally mountedrespectively on the pins 59.

Each of the three poles includes a line terminal strap 60 secured to thebase 24 and accessible from one end of the casing of the circuit breakerand having a stationary contact 61 secured to an inner end portionthereof and engageable by a respective one of the movable contacts 48.Further, each of the poles includes a load terminal strap 62 secured tothe base 24 and accessible from the other end of the casing and having abimetallic strip member 64 and a heating strip member 65 secured to aninner end portion thereof.

In accordance with the invention, each bimetallic strip member 64 liesbetween its associated terminal strap 62 and heating strip member 65,and each bimetallic strip member 64 and its associated heating stripmember 65 extend from their fixed end portions at the inner end portionof their associated terminal strap 62 generally in the same directiontheir associated terminal strap 62 extends from its inner end portion.Each bimetallic strip member 64 thereby has its associated terminalstrap 62 and heating strip member 65 disposed relatively closely theretoon opposite sides thereof so as to respond rapidly to radiant heatgenerated by tlow of electrical current through the terminal strap 62and heating strip member 65. Each bimetallic strip member 64 is alsoheated by conduction due to the flow of electrical current through itsfixed end portion. The particular arrangement is especially useful incircuit breakers with current ratings high enough to make it impracticalto pass the current through the entire length of the bimetallic stripmembers.

Each heating strip member 65 is electrically connected to a respectivecontact arm 47 by a pair of exible cables 66. The free end portion ofeach bimetallic strip member 64 is adapted to engage the strip bar 57and pivot it clockwise as viewed in FIGS. 4 and 5 upon sustained flow ofmoderate overload current through its respective pole of the circuitbreaker 20, thereby releasing the intermediate latch member 54 from thelatch plate 56 and the trip lever 34 from the intermediate latch member54 to effect movement of the contacts 48 in all three poles to openposition.

Each pole space includes a generally U-shaped magnetizable core member67 the bight portion of which is disposed beneath the respectiveterminal strap 62 and held in spaced relationship thereto by a leafspring member 68. Each pole space also includes a multipurpose bracket70, an armature rod 71, an armature 72, an actuating member 73, and anarmature return spring 74. Each armature 72 is secured in place on itsrespective armature rod 71, and each actuating member 73 is threadedlymounted on an end of its respective armature rod 71. Each armature rod71 and its associated armature 72 and actuating member 73 therebyreciprocate as unit, the actuating member 73 being guided in itsassociated bracket 70 and the armature rod 71 being guided at the endportion thereof opposite its associated actuating member 73 in itsassociated terminal strap 62. Each spring '74 is hooked at one end toits associated armature 72 and at the other end to its associatedbracket 70. Upon flow of severe overload current through any one of theterminal straps 62, magnetic flux established in its associated coremember 67 attracts the associated armature '72 and the associatedactuating member 73 pivots the trip bar 57 clockwise as viewed in FIGS.4 and 5, thereby releasing the intermediate latch member 54 and the triplever 34 to effect movement of the contacts 48 in all three poles toopen position.

In accordance with the invention, and as best shown in FIGS. 6 to l1,the air-gap adjusting crossbar 29 controls the position of each of thearmatures 72 with respect to its associated core member 67, and thuscontrols the air gap therebetween. The crossbar 29 is pivotally mountedin two of the three brackets 70, in flange portions 7051 thereof, asbest shown in FIGS. 6 and 7, and is provided with three round-headedscrew members 76, one in each pole space. Each screw member 76 isengageable with the actuating member 73 in its pole space. As previouslymentioned, the control member 28 is accessible from the outside of thecover 21. An arrowshaped slot 28a (FIG. 8) is provided in an outer endportion of the control member 28 for reception of a screwdriver (notshown), the arrowhead cooperating with the HI and LO indicia (FIG. 1) onthe cover 21. The outer end portion of the control member 28 ispivotally mounted in the cover 21, and an intermediate portion and aninner end portion of the control member 28 are respectively pivotallymounted in liange portions 70h vand 70e, of one of the brackets 70, asbest shown in FIG. 7. A compression spring 77 surrounding the controlmember 28 and disposed between the cover 21 and an enlarged portion 28bof the control member 28 establishes friction between the control member28 and the bracket 70 so that the control member 28 is maintained in anadjusted setting thereof. Pivotal movement of the control member 28 islimited by a stop portion 28e which cooperates with a tongue portion'70d of the associated bracket 70. A cam member 78 is keyed to thecontrol member 28 by a at portion 28d (FIG. 8) provided on the controlmember 28. The cam member 78 cooperates with and pivotally adjusts theair-gap adjusting crossbar 29, as best shown in FIGS. 9 and l0. Thescrew members 76 on the crossbar 29 thereby respectively adjust thepositions of the actuating members 73 and the spacing of the armatures72 from their respective core members 67. l

1. A multipole electric circuit breaker comprising a molded casinghaving a plurality of elongated longitudinally side-by-side compartmentstherein, a plurality of stationary contacts disposed respectively insaid compartments, a plurality of elongated contact arms pivotallymounted respectively in said compartments, a plurality of movablecontacts disposed respectively in said compartments, each of saidmovable contacts being secured to a respective one of said contact armsand being engageable with a respective one of said stationary contacts,an

elongated contact larm crossbar disposed in said casingV and extendingtransversely of said compartments, means operatively connecting saidcontact arm crossbar to each of said contact arms, a releasablylatchable trip lever pivotably mounted in one of said compartments andreleasable fro a latcii position of effect separation of said movablecontacts respectively from said stationary contacts, means in said onecompartment operatively connecting said tr-ip lever and said contact armcrossbar, an elongated trip bar mounted in said casing and extendin'gtransversely of saidcompartments, said trip bar normally being eilectiveto maintain said trip lever in a latched position and being pivotable toeffect release of said trip lever, a plurality of elongated terminalstraps each having an inner endl portion disposed in a respective oneVof said compartments and an outer end portion extending out of itsrespective compartment adjacent an end of said casing, a plurality ofma-gnetizable core members disposed respectively in said compartments inelectromagnetic relationship respectively with said terminal strapswhereby ow ofcurrent through each of said terminal straps establishesmagnetic flux in its associated core member, a plurality of armaturemembers disposed respectively in said compartments in spacedrelationship respectively to said core members, each of said armaturemembers being biased away `from its associated core member and beingattractable thereto upon ow of severe overload current through itsassociated terminal strap, a plurality of actuating members disposedrespectively in said compartments, means operatively connecting saidactuating members respectively to said armature members, each of saidactuating members being engage/able with said trip bar upon beingattracted toward its asSociated core member tol pivot said trip bar Iandeiect release of said trip lever, a movable elongated air-gap adjustingcrossbar disposed in said casing and extending transversely of saidcompartments, means operatively connecting said air-gap adjustingcrossbar to each of said armature members, an adjustable air-gap controlmember disposed in said c-asing, said casing having an aperture thereinproviding access to said control member from said outside said casing,means operatively connecting said control member to said air-gapadjusting crossbar whereby adjustment of said control membersimultaneously adjusts the spacing between each of said armature membersand its associated core member, a plurality of bimetallic strip membersdisposed respectively in said compartments, each of said bimetallicstrip members having a xed end portion secured to the inner end portionof a respective one of said terminal straps and an opposite free endportion engageable with said trip bar upon sustained flow of moderateoverload current through its associated terminal strap to pivot saidtrip bar and effect release of said trip lever, a plurality of heatingstrip members dis posed respectively in said compartments, each of saidheating strip members having a fixed end portion secured to the xed endportion of a respective one of said bimetallic strip members and anopposite free end portion, and a plurality of flexible conductorsdisposed respectively in said compartments, each of said flexibleconductors electrically connecting the free end portion of a respectiveone of said heating strip members to a respective one of said contactarms, and each of said bimetallic strip members and its associatedheating strip member extending from their xed end portions generally inthe same direction their associated terminal strap extends from itsinner end portion, whereby each of said Ibimetallic strip members hasits associated terminal strap disposed relatively closely thereto on oneside thereof and has its associated heating strip member disposedrelatively closely thereto on the other side thereof so as to be heatedalong it-s length relatively rapidly by radiant heat from itslassociated terminal strap and heating strip member upon sustained flowof moderate overload current therethrough as well as by heat ofconduction at its xed end portion.

2. A multipole `electric circuit breaker comprising a molded casinghaving a plurality of elongated longitudinally` side-by-sidecompartments therein, a plurality of stationary contacts disposedrespectively in said compart- Cil ments, a plurality of elongatedcontact arms pivotally mounted respectively in said compartments, aplurality of movable contacts disposed respectively in saidcompartments, each of said movable contacts being secured to arespective one of said contact arms and being engageable with arespective one of said stationary contacts, an elongated contact armcrossbar disposed in said casing and extending transversely of saidcompartments, means operatively connecting said contact arm crossbar toeach of said contact arms, a releasably latchable trip lever pivotallymounted in one of said compartments and releasable from a latchedposition to ettect separation of said. movable contacts respectivelyfrom said stationary contacts, means in said one compartment operativelyconnecting said trip lever and said contact arrn crossbar, an elongatedtrip bar mounted in said casing and extending transversely of saidcompartments, said trip bar normally being eiective to maintain said`trip lever in a latched position and being pivotable to effect releaseof said trip lever, a plurality of elongated terminal straps each havingan inner end portion disposed in a respective one of said compartmentsand an outer end portion extending out of its respective compartmentadjacent an end of said casing, a plurality of magnetizable core membersdisposed respectively in said compartments in electromagneticrelationship respectively with said terminal straps whereby llow ofcurrent through each of said terminal straps establishes magnetic ux inits associated core member, a plurality of armature members disposedrespectively in said compartments in spaced relationship respectively tosaid core members, each of said armature members being biased away fromits 'associated core member and being attractable thereto upon flow ofsevere overload current through its associated terminal strap, aplurality of actuating members disposed respectively in saidcompartments, means operatively connecting said actuating membersrespectively to said armature members, each of said actuating membersbeing engageable with said trip bar upon being attracted toward itsassociated core member to pivot said trip bar and effect release of saidtrip lever, a movable elongated air-gap adjusting crossbar disposed insaid casing and extending transversely of said compartments, meansoperatively connecting said air-gap adjusting crossbar to each of saidarmature members, an adjustable air-gap control member disposed in saidcasing, said casing having an aperture therein providing access to saidcontrol member from outside said casing, and means operativelyconnecting said control member to said air-gap adjusting crossbarwhereby adjustment of said control member simultaneously adjusts thespacing between each of said armature members and its associated coremember.

3. The multipole electric circuit breaker comprising a molded casinghaving a plurality of elongated longitudinally side-by-side compartmentstherein, a pluraltiy of stationary contacts disposed respectively insaid compartments, a plurality of elongated contact arms pivotablymounted respectively in said compartments, a plurality of movablecontacts disposed respectively in said compartments, each of saidmovable contacts being secured to a respective one of said contact armsand being engageable with a respective one of said stationary contacts,an elongated contact arm crossbar disposed in said casing and extendingtransversely of said compartments, means operatively connecting saidcontact arm crossbar to each of said contact arms, a releasablylatchable trip lever pivotably mounted in one of said compartments andreleasable from a latched position to effect separation of said movablecontacts respectively from said stationary contacts, means in said onecompartment operatively connecting said trip lever and said contact armcrossbar, an elongated trip bar mounted in said casing and extendingtransversely of said compartments, said trip bar normally beingeffective to maintain said trip lever in a latched position and beingpivotable to effect release of said trip lever, a plurality of elongatedterminal straps each having an inner end portion disposed in arespective one of said compartments and an Outer end portion extendingout of its respective compartment adjacent an end of said casing, aplurality of bimetallic strip members disposed respectively in saidcompartments, each of said bimetallic strip members having a xed endportion secured to the inner end portion of a respective one of saidterminal straps and an opposite free end portion engageable with saidtrip bar upon sustained flow of moderate overload current through itsassociated terminal strap to pivot said trip bar and effect release ofsaid trip lever, a plurality of heating strip members disposedrespectively in said compartments, each of said heating strip membershaving a xed end portion secured to the fixed end portion of arespective one of Said bimetallic strip members and an opposite free endportion, and a plurality of flexible conductors disposed respectively insaid compartments, each of said flexible conductors electricallyconnecting the free end portion of a respective one of said heatingstrip members to a respective one of said contact arms, and each of saidbimetallic strip members and its associated heat strip member extendingfrom their fixed end portions generally in the same direction theirassociated terminal strap extends from its inner end portion, wherebyeach of said bimetallic strip members has its associated terminal strapdisposed relatively closely thereto on one side thereof and has itsassociated heating strip member disposed relatively closely thereto onthe other side thereof so as to be heated along its length relativelyrapidly by radiant heat from its associated terminal strap and heatingstrip member upon sustained flow of moderate overload currenttherethrough as well as by heat of conduction at its lixed end portion.

4. A multipole electric circuit breaker as claimed in claim 1, includinga plurality of pins disposed respectively in said compartments, saidcontact arms being pivotably mounted on said pins and said pins beingcarried by said contact arm crossbar,

5. A multipole electric circuit breaker as claimed in claim 2, includinga plurality of pins disposed respectively in said compartments, saidcontact arms being pivotably mounted on said pins and said pins being carpied by said contact arm crossbar.

6. A multipole electric circuit breaker as claimed in claim 2, whereinsaid air-gap adjusting crossbar is pivotably mounted in said casing andwherein said actuating members are movable by said air-gap adjustingcrossbar to move said armature members.

References Cited UNITED STATES PATENTS 3/1954 Cole 335-23 5/1966 Gryctkoet al 20G-122

2. A MULTIPOLE ELECTRIC CIRCUIT BREAKER COMPRISING A MOLDED CASINGHAVING A PLURALITY OF ELONGATED LONGITUDINALLY SIDE-BY-SIDE COMPARTMENTSTHEREIN, A PLURALITY OF STATIONARY CONTACTS DISPOSED RESPECTIVELY INSAID COMPARTMENTS, A PLURALITY OF ELONGATED CONTACT ARMS PIVOTALLYMOUNTED RESPECTIVELY IN SAID COMPARTMENTS, A PLURALITY OF MOVABLECONTACTS DISPOSED RESPECTIVELY IN SAID COMPARTMENTS, EACH OF SAIDMOVABLE CONTACTS BEING SECURED TO A RESPECTIVE ONE OF SAID CONTACT ARMSAND BEING ENGAGEABLE WITH A RESPECTIVE ONE OF SAID STATIONARY CONTACTS,AN ELONGATED CONTACT ARM CROSSBAR DISPOSED IN SAID CASING AND EXTENDINGTRANSVERSELY OF SAID COMPARTMENTS, MEANS OPERATIVELY CONNECTING SAIDCONTACT ARM CROSSBAR TO EACH OF SAID CONTACT ARMS, A RELEASABLYLATCHABLE TRIP LEVER PIVOTALLY MOUNTED IN ONE OF SAID COMPARTMENTS ANDRELEASABLE FROM A LATCHED POSITION TO EFFECT SEPARATION OF SAID MOVABLECONTACTS RESPECTIVELY FROM SAID STATIONARY CONTACTS, MEANS IN SAID ONECOMPARTMENT OPERATIVELY CONNECTING SAID TRIP LEVER AND SAID CONTACT ARMCROSSBAR, AN ELONGATED TRIP BAR MOUNTED IN SAID CASING AND EXTENDINGTRANSVERSELY OF SAID COMPARTMENTS, SAID TRIP BAR NORMALLY BEINGEFFECTIVE TO MAINTAIN SAID TRIP LEVER IN A LATCHED POSITION AND BEINGPIVOTABLE TO EFFECT RELEASE OF SAID TRIP LEVER, A PLURALITY OF ELONGATEDTERMINAL STRAPS EACH HAVING AN INNER END PORTION DISPOSED IN ARESPECTIVE ONE OF SAID COMPARTMENTS AND AN OUTER END PORTION EXTENDNGOUT OF ITS RESPECTIVE COMPARTMENT ADJACENT AN END OF SAID CASING, APLURALITY OF MAGNETIZABLE CORE MEMBERS DISPOSED RESPECTIVELY IN SAIDCOMPARTMENTS IN ELECTROMAGNETIC RELATIONSHIP RESPECTIVELY WITH SAIDTERMINAL STRAPS WHEREBY FLOW OF CURRENT THROUGH EACH OF SAID TERMINALSTRAPS ESTABLISHES MAGNETIC FLUX IN ITS ASSOCIATED CORE MEMBER, APLURALITY OF ARMATURE MEMBERS DISPOSED RESPECTIVELY IN SAID COMPARTMENTSIN SPACED RELATIONSHIP RESPECTIVELY TO SAID CORE MEMBERS, EACH OF SAIDARMATURE MEMBERS BEING BIASED AWAY FROM ITS ASSOCIATED CORE MEMBER ANDBEING ATTRACTABLE THERETO UPON FLOW OF SEVERE OVERLOAD CURRENT THROUGHITS ASSOCIATED TERMINAL STRAP, A PLURALITY OF ACTUATING MEMBERS DISPOSEDRESPECTIVELY IN SAID COMPARTMENTS, MEANS OPERATIVELY CONNECTING SAIDACTUATING MEMBERS RESPECTIVELY TO SAID ARMATURE MEMBERS, EACH OF SAIDACTUATING MEMBERS BEING ENGAGEABLE WITH SAID TRIP BAR UPON BEINGATTACTED TOWARD ITS ASSOCIATED CORE MEMBER TO PIVOT SAID TRIP BAR ANDEFFECT RELEASE OF SAID TRIP LEVER, A MOVABLE ELONGATED AIR-GAP ADJUSTINGCROSSBAR DISPOSED IN SAID CASING AND EXTENDING TRANSVERSELY OF SAIDCOMPARTMENTS, MEANS OPERATIVELY CONNECTING SAID AIR-GAP ADJUSTINGCROSSBAR TO EACH OF SAID ARMATURE MEMBERS, AN ADJUSTABLE AIR-GAP CONTROLMEMBER DISPOSED IN SAID CASING, SAID CASING HAVING AN APERTURE THEREINPROVIDING ACCESS TO SAID CONTROL MEMBER FROM OUTSIDE SAID CASING, ANDMEANS OPERATIVELY CONNECTING SAID CONTROL MEMBER TO SAID AIR-GAPADJUSTING CROSSBAR WHEREBY ADJUSTMENT OF SAID CONTROL MEMBERSIMULTANEOUSLY ADJUSTS THE SPACING BETWEEN EACH OF SAID ARMATURE MEMBERSAND ITS ASSOCIATED CORE MEMBER.